Automatization of tasks within industry has led to industry robots being used to a larger extent. Cost savings and work environment improvements are two of the main reasons for this development.
An industrial robotics system consists of a number of stiff arms being connected to each other and together forming a turnable chain. These arms are movable or turnable in relation to each other. Movement or turning of the arms is controlled by drive units.
The drive units are in traditional industrial robotics systems alternating voltage motors which are controlled by motor control units which are commonly fed with direct current over a DC intermediate link, and which converts the direct voltage to a pulse width modulated alternating voltage which is used to control the speed of the drive units.
When a robot arm is retarded the function of the drive unit transforms to act as a generator, so called generatoric operation, which causes a voltage increase in the DC intermediate link and thereby electric surplus energy. In order to secure that this voltage does not exceed a predetermined threshold, in the traditional industrial robotics system a so called “electric motor brake” is arranged, which in the traditional case comprises a resistor control unit that connects a brake resistor (together called a “brakechopper”), whereby the electric surplus energy is transformed into heat. In a certain type of traditional industrial robotics systems, the total surplus effect when the drive units of the industrial robotics system are being retarded may for a short while measure 50 kW.
US 2004/0227479 A1 describes a system in which a brake resistor has been connected in between one of the conductors in the DC intermediate link and a resistor control unit, which is connected to the second conductor in the DC intermediate link. A control module detects if the voltage level in the DC intermediate link exceeds a predetermined level and if electric surplus energy exists in the system. In the case where the voltage level exceed the predetermined level, the resistor control unit is re-connected so that both of the conductors in the DC intermediate link are short-circuited over the brake resistor, whereby the surplus energy transforms into heat energy. A problem with this system is that a heat increase around the industrial robotics system results in a life time reduction of drive units and control units. Furthermore, the energy loss that occurs when the brake resistor is connected is very costly.
U.S. Pat. No. 6,815,915 describes a device which is intended to partly solve the problems mentioned above by using a capacitor battery as a brake unit and energy buffer. However, this type of device is most suitable for smaller systems such as for example yarn feeders for textile machines, since large capacitor batteries are very expensive.